Disc Drive Servo Loop With PMDA Filters for Vibration Attenuation
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Solution Overview
Problem
Hard disc drives (HDDs) face challenges in maintaining accurate head positioning due to vibration-induced disturbances, which result in repeatable and non-repeatable runout errors, especially in densely packed environments where fan harmonics and acoustic transmissions contribute to frequency-varying disturbances.
Innovation Solution
The implementation of a servo loop with phase-matching disturbance attenuation (PMDA) filters and peak frequency detection filters (PFDFs) that produce vibration-cancellation signals to refine position error signals, combined with adaptive PMDA filters to address frequency-varying disturbances, thereby improving track following accuracy.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If traditional servo loops are used for head positioning, then the system structure is simple, but vibration-induced disturbances cause poor head positioning accuracy
Solution Approach 1:
The patent introduces PMDA filters as intermediary components in the servo loop. These filters receive the raw PES signal and generate vibration-cancellation signals that are combined with the raw PES to produce refined PES. The filters act as mediators that selectively attenuate vibration-induced disturbances at specific frequencies while preserving the essential positioning information, thereby improving head positioning accuracy without requiring complete redesign of the servo loop architecture.
Solution Approach 2:
The patent segments the disturbance attenuation function by implementing multiple PMDA filters, each targeting specific frequency ranges or types of vibrations. The servo loop is divided into distinct functional blocks: sensor, raw PES generation, multiple PMDA filters for different disturbance frequencies, and refined PES generation. This segmentation allows each filter to specialize in attenuating particular vibration modes while maintaining overall system simplicity.
2Measurement precision
If disturbance attenuation filters are added to reduce vibrations, then head positioning accuracy improves, but the device complexity increases
Solution Approach 1:
The patent implements adaptive PMDA filters that dynamically adjust their characteristics based on the detected disturbance frequencies. The system continuously monitors the vibration environment and modifies the filter parameters in real-time to match the current disturbance profile. This dynamic adaptation allows the filters to maintain high effectiveness across varying operating conditions without requiring a fixed complex structure for all possible scenarios.
Solution Approach 2:
The patent changes the parameters of the PMDA filters based on the detected disturbance characteristics. By adjusting filter coefficients, cutoff frequencies, and attenuation levels according to the specific vibration profile, the system optimizes disturbance rejection while avoiding the need for overly complex fixed-structure filters. The parameter changes are driven by real-time analysis of the position error signal and disturbance patterns.
3Object-affected harmful factors
If notch filters are used to attenuate specific frequencies, then those frequencies are reduced, but nearby frequencies are amplified
Solution Approach 1:
The patent extracts only the necessary disturbance attenuation function from traditional notch filters. Instead of using broad-notch filters that affect wide frequency ranges, the PMDA filters are designed to target and remove only the specific vibration frequencies that are harmful, while leaving adjacent frequencies untouched. This selective extraction of the attenuation function eliminates the side effect of nearby frequency amplification.
Solution Approach 2:
The patent applies local quality by designing PMDA filters with frequency-selective attenuation characteristics that are optimized for specific disturbance frequencies. Each filter is tailored to address particular vibration modes detected in the environment, providing localized attenuation exactly where needed without affecting other frequency regions. This localized approach prevents the collateral amplification of nearby frequencies that occurs with traditional notch filters.
4Reliability
If fixed-frequency filters are used, then they work well for constant disturbances, but they fail when disturbance frequencies change
Solution Approach 1:
The patent transforms fixed-frequency filters into dynamic, adaptive filters that continuously adjust their characteristics based on the detected disturbance environment. The adaptive PMDA filters monitor the position error signal for changing vibration patterns and automatically modify their attenuation frequencies and levels in real-time. This dynamic behavior maintains reliable disturbance attenuation across varying operating conditions, fan speeds, and acoustic environments.
Solution Approach 2:
The patent implements feedback mechanisms where the output of the servo loop and disturbance detection systems are fed back to continuously adjust the PMDA filter parameters. The system uses the refined PES and disturbance analysis as feedback signals to adaptively tune the filter characteristics, ensuring that the attenuation remains effective even when disturbance frequencies change due to varying fan speeds, acoustic conditions, or mechanical vibrations.
Data Source
AI summary
A data storage drive includes a servo loop for positioning a head over a disc. The servo loop includes a sensor, located in the head, that senses servo information located on the disc and produces a servo signal therefrom. The servo signal is combined with a reference signal to produce a raw position error signal (PES). The servo loop further also at least one phase-matching disturbance attenuation (PMDA) filter that receives the raw PES as an input and responsively outputs a vibration-cancellation signal, which, when combined with the raw PES, cancels vibration-induced disturbance from the raw PES, thereby producing a refined PES. A servo controller receives the refined PES and responsively produces a servo control signal. An actuator moves the head in response to receiving the servo control signal.